This study is designed to examine polysomnographic variables, especially REM latency, as factors associated with vulnerability for depression in high risk individuals. Unipolar nonpsychotic depressed probands, aged 20-40, will be studied in the sleep laboratory and will be assigned to one of two groups defined by mean REM latency: REM latency < 65.0 minutes (n = 10); REM latency > 70.0 minutes (n = 10). A third group will consist of normal control probands (n = 5), who have no personal or family history of affective disorders, matched to reduced REM latency unipolar probands. At least four first-degree relatives, two parents and at least two siblings, for each depressed and normal proband will be studied in the sleep laboratory and assessed by psychiatric interview. This sample, combined with the sample from the first grant period, will provide 165 first-degree relatives of 50 unipolar depressed probands; half the families will be defined by a reduced REM latency proband. We will also have 20 normal proband families with 80 first-degree relatives. Offspring >6 years of age from probands and siblings will be studied in the sleep laboratory and with psychiatric interviews. We will follow prospectively all relatives, adults and children, studied in the sleep laboratory, at 12 month intervals. Relatives who report an affective disorder during the follow up period will be reassessed in the sleep laboratory. We predict that 1) reduced REM latency will assort in families defined by a reduced REM latency proband; 2) reduced REM latency will be associated with a) an increased lifetime prevalence of affective disorder and b) increased probability of developing depression in follow up among those relatives who were never ill; 3) lifetime prevalence of unipolar depression will be equivalent between parents and adult offspring with reduced REM latency but nonreduced REM latency adult offspring will show higher rates of affective disorder than their parents (secular trend); 4) offspring of affected parents will show polysomnographic abnormalities will have an increased probability of developing depression in follow up.